1. Field of the Invention
The present invention relates to a sound absorbing-insulating structure, which absorbs and insulates noisy sound, for vehicles and, more particularly, a sound absorbing-insulating structure used as a dash insulator, a ceiling member, a floor insulator, a parcel board, various trims, etc. in the vehicle.
2. Description of the Related Art
In recent years, with the higher quality and the higher performance of the vehicle and the improvement in the consciousness of the urban environment, the requests for the silence in the interior and the noise on the outside of the vehicle become increasingly severe. As the sound absorbing-insulating parts employed currently in the vehicle, there are the hood insulator, the dash insulator, the head lining, the floor insulator, etc. In order to respond to the above requests, the sound absorbing-insulating parts are employed to extend up to the parcel board, the trunk trim, and the engine cover in addition to these parts.
Low cost has been required for the sound absorbing-insulating material for the vehicle. For this reason, mainly the inorganic fiber such as the fiber felt, the rock wool, the glass wool, etc., the foam such as urethane, polyphenylene oxide/polystylene alloy, etc., the corrugated fiberboard, or their combination is employed as the sound absorbing-insulating material. These sound absorbing-insulating materials are inexpensive in cost, but it is impossible to say that they are always excellent in the sound absorbing performance.
In order to improve the sound insulating characteristic, weight or thickness of the sound absorbing material has been increased. However, this method is contradictory to the reduction in the vehicle weight that is requested from the viewpoints of the improvement of the fuel efficiency and the emission regulation. Therefore, In order to overcome these problems, the sound absorbing-insulating material employing the nonwoven fabric of polyester fibers has been developed (Japanese Patent Application Publications Hei 5-181486 (published in 1993), Hei 6-170997(published in 1994), and Hei 7-223478). But the subject still remains in a respect of the reduction in cost.
It is an object of the present invention to provide a sound absorbing-insulating structure for vehicles, that has the good sound absorbing characteristic and is light in weight and inexpensive in cost.
In order to achieve this object, an aspect of this invention is that a sound absorbing-insulating structure has a sound absorbing layer which contains cellulose fibers and synthetic resin as principal components. Also, it is preferable that a content rate of the synthetic resin should be set to 0.01 to 80 wt % and that a surface density should be set to 0.2 to 3 kg/m2. Here, the surface density means weight per unit are.
The cellulose fibers that have the high sound absorbing effect and the synthetic resin that has the adhesiveness and the high shape plastic effect can be mixed together, and also an amount of the synthetic resin and the surface density of the sound absorbing layer can be suppressed. Therefore, the sound absorbing-insulating structure can provide the high sound absorbing characteristic in low cost and lightweight.